weather

It's been a strange weather year in much of the U.S. I'm currently working on Hine's emerald dragonfly monitoring near Chicago, and have seen several examples already this summer of natural stochasm in action.

Through June, rainfall was well above normal. One site, on a river, flooded at least twice. Others, away from major watercourses, were wet but less extremely so. One storm in late June included high winds, severe enough to break tree branches, and probably to damage the fragile wings of dragonflies caught away from shelter.

Then the the rain just stopped for a couple of weeks, and water levels fell to what would be expected for mid-summer.

This morning another storm moved through. There were more fallen branches, more power outages, more heavy rain. Weather is expected to improve for the rest of the week, so we'll be right back out there to see what effect it's had.

Early in my dragonfly studies, I watched female Hine's emerald dragonflies oviposit in a range of locations from cool spring runs to warmer lower channels. Under normal conditions, the middle streamlet reaches are usually optimal habitat; the spring runs are too cool and slow development, and the lower resches are too warm and too prone to fish and other predation on larvae, as well as increased competition from other odonates.

Using the full length of the streamlet hedges bets, and ensures survival of some animals through drought, or flood, or "normal" conditions. In a stochastic floodplain environment, it's a logical strategy.

Too often when planning restoration projects we fail to account for stochasm. We target "normal" conditions, even though "normal" will not happen in some years. By designing restoration sites without allowing for stochasm, we could potentially doom some populations.

Chicago area dragonfly program

I'm leading a program on the federally endangered Hine's emerald dragonfly in mid-July, in the far southwest suburbs of Chicago. We did one of these last summer, and had quite a  crowd. As an added bonus, the program will be outdoors, at a nature preserve with high quality dolomite prairie and marsh communities. Details below:

Hine's Emerald Dragonfly Walk

Saturday, July 16

9 – 11 a.m.

Lockport Prairie

FREE! All Ages.

Registration required: 708.534.8499.

For a few weeks each year, the endangered Hine’s Emerald Dragonfly emerges along the banks of the DesPlaines River. A partnership of local industries, cities, and parks are working together to help protect this rare dragonfly. The Hine’s Emerald Dragonfly Habitat Conservation Program is offering a prairie walk in Lockport Prairie. Together with expert scientists, participants will investigate the unique habitat that is home to this and other rare and interesting plant and animal species. The tour will be on uneven natural terrain.  Please bring water and dress for sun, puddles, and bugs. Lightweight pants recommended.

dragonflies and vegetation structure

In the December 2010 issue of "Ecological Restoration" that hit my mailbox today, there's an article on dragonfly and damselfly species richness relative to vegetation structure. The study, by Catherine Mabry and Connie Dettman, was done in the prairie pothole region of Iowa.

The study is focused at a fairly fine scale, comparing stands of diverse plant composition to near-monotypic stands of reed canary grass and cattail. Not surprisingly, at least to me, odonate species richness was considerably higher in the diverse stands than in the monotypic ones: 30 percent higher, and 45 percent higher if looking only at species of conservation concern, which tend to have more specialized habitat requirements. The authors also had access to an earlier study conducted in one of the wetlands which had at that time been diverse, but since then had been invaded by reed canary grass. They were able to document a loss of both damselfly and dragonfly species in the intervening years.

Publication of the article is timely, because I've been involved in similar issues in Illinois. There, we've watched a once diverse wetland complex gradually lose sedge meadow and graminoid fen habitat to cattail encroachment. Reed canary grass is common too, although the extent hasn't really changed in the 16 years of observations available to me, which suggests that the encroachment of that species happened much earlier.

I've been looking at a coarser scale than Mabry and Dettman, because I'm working with a large, strong-flying species, the Hine's emerald dragonfly. As early as 1998, we documented a correlation to habitat interspersion. Over 40 percent of our observations were in sedge meadow, which constituted less than 10 percent of the habitat on the site. Observations also tended to be close to an edge between low-growing sedge meadow and much taller marsh. Thus, I'm looking at the physical structure of the entire complex of habitat types. Mabry and Dettman touch briefly on this, but it's beyond the main scope of their study.

It's very valuable data. It's common knowledge that structurally diverse habitat supports more diverse animal assemblages, but it took me longer than it should have to get some otherwise knowledgable people to grasp the importance. In this case, the dragonfly species of interest is at reduced density for other reasons (a severe drought that peaked in 2005 and has since ended), but degradation of habitat structure may be hindering recovery of the species at the site. Having quantitative data available from a nearby region makes it easier to build a case for aggressive habitat management.

the land has a story to tell

Last month I visited a friend in Springfield, Ohio. Driving out from Chicago, I chose not to take the Interstate, and took smaller roads instead. Coming in from the northwest, entering Logan County, I recalled that there had once been a Hine's emerald dragonfly locality nearby.

The next morning I found time to go online and do a little searching. My memory had been accurate; the type locality had been in Logan County, near Indian Lake. That's about all I was able to find without getting back to my files which were 2,000+ miles away. So at the end of the trip, I did enough recon to get a sense of the land north of Springfield (more on that later) and filed it away for future action.

This morning at the office I was working on an entirely different aspect of the Hine's emerald dragonfly, which is a federally endangered species. Mostly it was number crunching, calculating density estimates for a major field study I'd led in Illinois over the summer. There, a dozen or more Hine's emerald dragonfly populations persist while in Logan County Ohio no one has seen the species since 1930. However, in writing up a tech memo with todays analysis, I had occasion to pull out the original description of the species, published in 1931.

In that paper, E. B. Williamson provides an unusually thorough description (for that time) of the type locality. He says:

“Ohio State Road Number 117 crosses the North Fork of the Little Miami River north of Huntsville, Ohio. The North Fork is a small stream at the bridge, only a few feet wide and at the season we were there carrying but little water. From its source a mile or two above the bridge it meanders through open and pastured fields in an almost flat terrain of clay soil. Below the bridge there are some willows, adjacent thickets, a few trees, and long, dense growths of lizard-tail through which the water winds its way, often concealed by the abundant vegetation. This condition passes abruptly after about a quarter of a mile into a deep dredged channel about 20 feet wide, which extends into Indian Lake. The upper end of the dredged channel, possibly a quarter to a half mile in length, is in heavy swamp woods, winding through which is the old channel of the creek, now reduced to pools of greater or lesser length.

In this woods is a heronry which Professor Hine visited on June 7, 1929. Leaving the woods along its northern side where it adjoins a golf course, he saw a dragonfly hovering two or three feet above the ground in an open spot under a bush."

A week later, James S. Hine and C. H. Kennedy returned to the site:

“The day was rainy and apparently unfavorable. They failed to find any Somatochlora in the woods, but on visiting the dredged channel they were able to take five specimens resting on low bushes on the wood’s side of the high bank of earth thrown up by the dredge when the channel was dug."

A total of six specimens were collected in 1929, and only one in 1930 despite searches by a larger group. It appears that the dredge activity had recently disrupted the habitat, and that the collectors found the final remnants of a dying population.

On a 2006 Google Earth photo, the type locality is easy to locate. There is now a dredged channel to a point well above the bridge. North of the stream and west of SR 117 is a residential subdivision, and across from this is a narrow wooded band and then open farmland. Downstream is an extensive woodland extending all the way to Indian Lake, and within the woodland several old channel scars are visible. Depending on which channel was active in 1929, the specimens were collected either near the subdivision-woodland boundary, or a short distance into what is now woodland. There is currently no evidence of a golf course, although it’s possible that the subdivision occupies the former location.

Here's what I'm able to determine from Williamson's description, a look at that Google Earth photo, and (just now) a look at a detailed surficial geology map of the region:

The site is associated with the headwaters of the Great Miami River drainage, and specifically with the north fork;

Most of the surrounding land has been dramatically altered, with the possible exception of some woods on the downstream end that don't appear to be of very good quality;

The North Fork appears to be much more extensively dredged now than in 1930;

As with most other known Hine's emerald dragonfly localities, the site is underlain by dolomite bedrock. Unlike most of those other sites, at the Logan County locality the bedrock is covered by anywhere from 150 to 250 feet of glacial till, outwash, and alluvium;

Sand and gravel outwash deposits just north of the channel appear to be the most likely source of groundwater, however the site appears to be relatively level;

Organic deposits are prevalent between SR 117 and Indian Lake in the vicinity of the channel, with alluvium up channel and till to the south;

There is no evidence of suitable remaining habitat anywhere in the immediate vicinity of the type locality.

Chasing down additional detail would most likely require a return visit to Ohio. The oldest photos I can find online date to 1994, and these show conditions similar to those in the 2006 photo mentioned above. Normally, air photos are available from as early as the mid to late 1930s, and getting a look at these, and at any slightly older maps of the area, would be among the highest priorities to reconstruct historic conditions. Of course, there's no substitute for actually walking the land.

What little I've learned thus far has raised some interesting questions. First, this place is quite different than the other populations I've visited. Understanding the type locality may shed light on the overall habitat requirements of the species, and may assist with restoration efforts elsewhere.

Would restoration be possible at the type locality? In theory, probably. In practice, any serious attempt to restore hydrology might very well flood the adjacent subdivision. There is also, as far as I can tell, no publicly owned land to start from. Then there are the genetic issues, with the nearest source populations hours away by car.

Next, some thoughts on what I saw during my too-brief visit to the area. In the meantime, there's more on the Hine's emerald dragonfly on my web site